For the treatment of exhaust gases of combustion engines substrates having open or closed channels or combinations of those is used. In open channels the exhaust gas is directly flowing through the substrate. In substrate having closed channels exhaust gas is forced to flow through walls, e.g. through ceramic or metallic porous walls. In open channels reduction of gaseous impurities is often high but the reduction of impurity particles is low, e.g. from 10 to 15%. In closed channels the reduction of gaseous impurities is high and also the reduction of impurity particles is high, e.g. from 70 to 90%. The problem in closed channels is the clogging of walls. Closed channels will gradually wholly clog if it is not cleaned. Pressure loss will also increase. One way to keep the channels open is to clean them continuously or periodically.
One difficult situation is the starting the combustion engine using substrate having closed channels, which are partially clogged. The temperature of the said substrate is low in starting and particles are trapping on the surfaces. Eventually there are so many particles on surfaces of the walls that the fluid of exhaust gas is inhibited. In this situation it is possible that even the combustion engine can damage.
WO 03038248 A1 (published 8.5.2003) disclose a filter composite whereby a fluid can flow through the filter composite. It comprises at least one top layer made of an at least partially porous material with at least one edge area and comprises at least one fibrous layer made of a fibrous cloth. The filter composite is characterized in that at least one fibrous layer forms an enclosure that encloses the fibrous layer so that the fibrous layer is permanently arranged inside the at least one top layer.